Ion-beam deposition process for manufacturing multi-layered attenuated phase shift photomask blanks

Abstract

A single ion-beam deposition, or a dual ion-beam deposition process for fabricating attenuating phase shift photomask blanks capable of producing a phase shift of 180° and having an optical transmissivity of at least 0.001 at selected lithographic wavelengths <400 nm, comprising at least one layer of an optically transmitting and/or one layer of optically absorbing elemental or a compound material in a periodic or an aperiodic arrangement.

Description

[0001] This invention relates to manufacture of phase shift photomask blanks in photolithography, known in the art as the attenuating (embedded) type, using ion-beam deposition techniques. More specifically, this invention relates to attenuating phase-shift photomask blanks to be used with short wavelength (i.e., <400 nanometer) light, which attenuate and change the phase of transmitted light by 180.degree. relative to the incident light. Additionally, this invention relates to photomask blanks with multi-layered coatings of simple or complex compounds of elemental materials on the blanks.TECHNICAL BACKGROUND[0002] Microlithography is the process of transferring microscopic circuit patterns or images, usually through a photomask, on to a silicon wafer. In the production of integrated circuits for computer microprocessors and memory devices, the image of an electronic circuit is projected, usually with an electromagnetic wave source, through a mask or stencil on to a photosensitiv...

AI Technical Summary

Problems solved by technology

However, as the feature size decreases, resolution for imaging the minimum feature size on the wafer with a particular wavelength of light is limited by the diffraction of light.

Furthermore, the IBD process has the ability to independently control the deposition flux and the reactive gas ion flux (current) and energy, which are coupled and not independently controllable in planar magnetron sputtering.

While magnetron sputtering is extensively used in the electronics industry for reproducibly depositing all sorts of coatings, process control in sputtering plasmas is not accurate because the direction, energy, and flux of the ions incident on the growing film cannot be regulated.

For the "assist" ions, lower energy typically <500 eV are preferred, otherwise the ions may cause undesirable etching or removal of the film.

While it is possible to make films with complex chemistry such as Si.sub.3N.sub.4, with ion beam deposition using a single ion source the process is more restrictive than for dual ion beam deposition.

Huang et al. in "Structure and composition studies for silicon nitride thin films deposited by single ion beam sputter deposition" Thin Solid Films 299 (1997) 104-109, demonstrated that films with Si.sub.3N.sub.4 properties only form when the beam voltage is in a narrow range about 800 V. Although a nitride target can be used at the outset with a single ion source to improve process latitude, the deposition rate can be impracticably slow and the purity of a nitride target is generally inferior to an elemental target.

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